Investigators have found that a helicopter involved in a deadly crash with a passenger plane over Washington was flying above its height limit. The helicopter's altitude-measuring instrument was also inaccurate.

The National Transportation Safety Board on Thursday questioned the failure of an air traffic controller to issue a warning about a potential collision in the moments before a crash between an Army helicopter and an American Airlines regional jet that killed 67 people.

The board focused on air traffic control and heard it was common for pilots to ask to use visual separation — relying on eyesight — just as the Army Black Hawk’s pilot agreed to do the night of the crash.